Diabetes Health

Dementia Risk for Older People Increased by Low Blood Sugar

Older individuals with type 2 diabetes who have been hospitalized with severe low blood sugar levels seem to have a greater risk of developing dementia, new research suggests.

It is not yet clear whether the more common, less severe episodes of low blood sugar are also linked with an increased dementia risk, according to a study in the April 15 issue of the Journal of the American Medical Association.

"Hypoglycemic episodes that were severe enough to require hospitalization or an emergency-room visit were associated with a greater risk of dementia, particularly for patients who had multiple episodes. And these findings, a little bit to our surprise, were independent of glycemic control," says study author Dr. Rachel A. Whitmer, of Kaiser Permanente.

"Episodes of hypoglycemia may be associated with neurological consequences in patients already at risk for dementia," she adds. "This study seems to suggest that hypoglycemia is one of the reasons people with type 2 diabetes are at a higher risk for dementia. It also adds to the evidence base that balance of glycemic control is a critical issue, and particularly for the elderly."

Experts Debate Cause and Effect

People with type 2 diabetes are at a 32 percent greater risk for dementia, although the reasons for that are not clear. People with pre-diabetes are also at greater risk, adds Dr. Whitmer.

However, the study looks at association only, and does not actually prove a causal relationship between the two conditions, notes Dr. Nir Barzilai, director of the Institute for Aging Research at Albert Einstein College of Medicine and the Montefiore Hospital Diabetes Clinic in New York City.

"It could be fluctuation of glucose. We know that hyperglycemia [high blood sugar] is also very toxic to the cells. All those things cannot be dissected on a study like this," he says.

Dr. Whitmer adds that it is likely hypoglycemia only one reason for the heightened risk of dementia in individuals with type 2 diabetes.

While previous studies have linked cognitive impairment in children and adults with type 1 diabetes, it is not clear whether the same link applies to older individuals with type 2 diabetes or what mechanism might be underlying such a connection.

The issue is an important one as the population people with type 2 diabetes continues to grow. In the US alone, some 24 million people have the condition. More are expected as the population ages.

Hypoglycemic episodes are marked by dizziness, fainting, and seizures.

The study authors followed more than 16,000 patients with type 2 diabetes, average age 65, from 1980 to 2007. Twenty-two years of follow-up were devoted to chronicling hypoglycemic episodes, and more than four years were devoted to following dementia diagnoses.

Nerve Cell Loss, Blood Supply Lowered

The link that was found could be from any number of possible causes, including accelerated death of nerve cells in the brain or less blood supply to the brain.

Such a link could also be a result of too much insulin over time, again possibly contributing to neuronal damage or other brain changes.

But the whole picture is likely to be much more complicated, says Dr. Barzilai.

"The glucose concentrations in the brain are much, much lower than in the [rest of the body], and it takes it a long time to actually adjust if you change the peripheral glucose for the brain to have lower glucose," he explains.

"Not only that, but the neurons in the brain are really not fed by glucose but by other metabolites. The rest of the body, when glucose goes down, will feel it. The brain is totally different story," says Dr. Barzilai.

Although balanced blood-sugar control is a good strategy in theory, it's difficult to attain and difficult to monitor.

"The trouble is, when you try to keep blood sugar in the normal range, there's a higher risk of hypoglycemia," says Michael Horseman, Pharm.D., at the Texas A&M Health Science Center. "There hasn't been a study that I'm aware of where they made a serious attempt to keep blood sugar in the normal range that didn't have episodes of hypoglycemia."

June 2009

Hypoglycemia Defined

Hypoglycemia is a condition characterized by a glucose (blood sugar) level that is too low to effectively fuel the body's blood cells.

Glucose is the main source of fuel for the body. According to the National Institute for Diabetes and Digestive and Kidney Diseases (NIDDK), the good range of blood sugar is approximately 60 to 120 mg/dL (milligrams of glucose per deciliter of blood). Blood sugar levels under 60 mg/dL are too low and are considered unhealthy.

Hypoglycemia may be a condition by itself, or may be a complication of diabetes or another disorder. It is most often seen as a complication of diabetes, which is sometimes referred to as insulin reaction.

Causes of hypoglycemia in people with diabetes may include the following:

too much medication

a missed meal

a delayed meal

too little food eaten as compared to the amount of insulin taken

Other causes of hypoglycemia are rare, but may occur in early pregnancy, after strenuous exercise, or during prolonged fasting. Hypoglycemia may also result from taking certain medications, abusing alcohol, or other rare causes.

The following are the most common symptoms of hypoglycemia:

shakiness

dizziness

sweating

hunger

headache

irritability

pale skin color

sudden moodiness or behavior changes, such as crying for no apparent reason

clumsy or jerky movements

difficulty paying attention, or confusion

tingling sensations around the mouth

The symptoms of hypoglycemia may resemble other conditions or medical problems.

In addition to a complete medical history and physician examination, certain blood tests are used to diagnose hypoglycemia.

When a person with diabetes has symptoms of hypoglycemia, then the cause is usually diagnosed as a complication of diabetes, or insulin reaction. It is often the result of the causes listed above.

For those who have symptoms of hypoglycemia and do not have diabetes, the disorder is diagnosed by measuring blood glucose levels while the person is experiencing the symptoms, observing that the symptoms are relieved when the person eats food with a high content of sugar, and performing laboratory tests to measure insulin production.

Always consult your physician for more information.

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